In consideration of fire under a floor of a railcar, the floor is required to have predetermined heat resistance (fire resistance) in some cases. One example of a fire resistant standard is an American fire resistant standard “ASTM (American Standard Test Method) E-119”. In the ASTM E-119, some provisions are made, and one example is that even if heat is continuously applied to a lower surface of a test body (floor) for a predetermined period of time, an increase in temperature on an upper surface of the test body is equal to or smaller than a certain value. A floor structure of a railcar produced in consideration of the above standard is proposed in, for example, PTL 1. To be specific, the floor structure described in PTL 1 is constituted by an upper layer, a middle layer, and a lower layer, and a heat insulating material layer is provided between the lower layer and the middle layer. According to the floor structure, since the heat insulating material layer is provided, a heat insulating effect of the floor can be improved (see PTL 1, page 2, lower left column, line 6 and subsequent lines).
Normally, the heat resistance can be improved by increasing the thickness of the heat insulating layer. However, if the thickness of the heat insulating layer is increased too much, a space under the floor narrows, so that the space for arranging cables and devices under the floor may not be secured. Here, PTL 2 proposes a floor structure of a linear motor car configured for the purpose of obtaining the same fire-resistant function as a conventional floor structure without reducing an installation space for devices and the like arranged under the floor. In this floor structure, a plate-shaped expansion-type heat insulating material is arranged so as to cover a lower surface of a floor panel and also cover respective surfaces of a side sill, a cross beam, and a center sill (see PTL 2, FIG. 4, for example). PTL 2 explains that: the expansion-type heat insulating material expands by the heat of a flame to form a heat insulating layer, so that the increase in temperature on the upper surface of the floor panel can be suppressed; and since the expansion-type heat insulating material is thinner than a conventional plate-shaped heat insulating material, the installation space for cables and the like is not reduced (see PTL 2, paragraph 0016).